Need an Electrical Engineer that speaks english!

[AKAMAC]

I'm trying to explain to our plant operators how VAR's are fed back into the power grid while we are still getting KW. We go from a . 75 lag PF at 300 KW generating to a . 2 lead PF at 600 KW generating. While at the upper KW we are still using about 100KW. We don't pay for excess VAR transmission to system during peak hours but our Gen bus will trip out if our KW output exceeds plant usage. Any simple explanations would be appreciated. Mike

 

[merryman]

I am not sure they exist!

Couple of weeks ago I was helping a friend wire in the remote controls for a gen. set in his fiver. His next door neighbor who is a retired electrical engineer came over to help.

He was totally useless! All he did was sit with the onan schematic and hem and haw, and talk in electrical gibberish.

When we tried to talk to him about such mundain things as which wire went where, all we got was blank looks.

We got the job done and he was still sitting puzzelling over the skematic.

His speciality was designing power substations; not much related to 12 volt control circuits.



Vaughn

 

[PJereb]

I don’t think explaining basic electricity to an operator is going to be a quick process.



But maybe this makes sense... . sorta...



1) Inductance is the property of an AC electric circuit that opposes any change in current flow. So if there is inductance the current lags the voltage, resulting in phase shift, and a lower (less efficient) power factor, unless inductive and capacitive load are balanced. Electric motors have a lot of inductance and so when people turn on their AC, and business run motors during the day, a lot of inductive load gets put on the system, and the power factor declines, as the current waveform lags the voltage.



2) Capacitance is the property of an AC electric circuit that opposes any change in voltage. So if there is capacitance, the current leads the voltage, resulting in phase shift, and a lower (less efficient) power factor, unless inductive and capacitive load are balanced. There are often underground or pole top capacitors that get closed into the grid during the day to correct the power factor from all the inductive load.



3) Power factor is the ratio of true power (volt amperes VA) to apparent power in a circuit. A power factor of 1 would be perfect and would only exist from a perfectly balanced inductive and capacitive load, or from a load consisting of only resistance.



4) VAR’s are a measure of wasted power.



So when you are generating power, you can adjust for power factor loss with your generator, and if the grid you are connected to has a lot of inductance , it may have a power factor of say . 73, and you can correct that with your generator by making the current waveform lead the voltage, pushing VAR’s back into the system, even though you are not generating as much power as you are consuming. I have never worked on generation, so I have no idea how it physically works, but maybe this will help.



Good luck trying to explain it!

Peter

(apprentice electrician, still figuring things out)

 

[AKAMAC]

Peter,

Not bad for,"apprentice electrician, still figuring things out",my own explaination used terms like "power factor correction caps for constant speed variable torque (load) applications. BLANK STARE. Or VFD applications on variable speed constant torque to balance PF. BLANK STARE. I might try using the waveform analogy Monday and see if I get anywhere.

The proplem I have is getting them to understand our "reverse power protective relay" failure and the fact that being at the end of grid feed causes voltage variances affecting current draw.



Vaughn, never let an EE wire anything! :~)





Mike

 

[Dane]

I'll take a shot at it



Think of it as a balloon that has a "working" pressure centered at . 5 psi when it's half full. Let's say the balloon, when "working" varies internal pressure between . 25 and . 75 psi. There is air in the balloon below . 25 psi that will escape when there is no more "work" to be done.

 

[ropinfool2]

I am not sure how your protective relay is set up or how your interconnect agreement is worded but the reason you get a trip on reverse power is when you export more power than the relay is programmed to allow. Normally the interconnect agreement spells out the settings for the protective relay. (All this info is based on my assumption you are a small producer, tied to the grid but producing either a portion or a majority of your own power with no export). The way VAR's was explained to me years ago was that in order to "push" the 365kV or 12kV (whatever voltage your grid is at) long distances, VAR's are needed. One plant I worked at would run only to provide VAR's to the grid, the utility had no use for the power they only needed the extra VAR's. They also paid a premium for them also. The plant I am currently at is pretty much what I described above. We provide a minimum of 80% power to our customer (a community college), they get the rest from the utility. I don't really think I answered your question but maybe???? it helped? Good luck. John

 

[AKAMAC]

John, the RP relay is for generator, not to grid. ie: If you feed power into the genset the alternator becomes a motor (bad for a 16 cyl methane engine). I explained the to the op's using Peters waveform theory, BLANK STARE.

I'm going to increase the the gain on our woodward controler for voltage matching. I had to decrease the gain for the Hz to stop the hunting before it went online. I figure if I can stop #2 from droping offline I won't have to blow up any ballons and bring my dogs and ponies to work. I figure that we're getting an increase in voltage from the grid and driving the PF down.



Dane, Please expand on your post, you might be onto something.



PS. John I lived in Ramona for a year, nice area you have there. Dane do you work for the SC WWTP?

 

[ropinfool2]

Yea I can see some bad things happening there. Which woodward do you have? I have two 12 cyl Waukesha's here with 2301D's. I also have a seperate voltage adjust knob on the front of the switch gear. I can use this to match my voltage to the utility, then after I am synched I use this knob to adjust my VAR output. I try and maintain slightly positive (outgoing) VARs. Good luck to you. John

 

[AKAMAC]

They are DSLC's and 723 speed control units on each genset linked with a MSLC.

I gave up on trying to teach basic electrical theory to ops, I guess I'm not smart enough to be a teacher. Guess I'll stick to fixing them. Thanks for the help. Mike

 

[klenger]

Are these guys serious or are they just making this stuff up? I thought I had a reasonable understanding of AC theory, but I don't understand a bit of what's being discussed here.



Let's talk about ARINC 419, 429, 561 , CSDB, and ASCB data buses for a while so I can jump in.

 

[PJereb]

Mike,

Did I see you driving to work today (7-14), going through Hayward and getting on 92 west, around 6:35am?





klenger,

This is all real, we're not making anything up, it sounds like greek to others, I am sure of that

 

[AKAMAC]

Das is I... You can see my truck in readers rigs... I do drive fast. Honk next time I'll buy you a cup o joe. Where you the red rig?



K it's all real, just sounds like BS. Mike

 

[PJereb]

Yep,

That’s me, the Red 3500 with the aluminum "cheese grater" over the back window.



I figured that was you, nice shell on your truck.



Luckily I work off of Clawiter in Hayward, so my drive isn’t too bad, I avoid the peninsula at all costs, went there twice this year, once to order my pickup, once to pick up my pickup.





Take it easy,

Peter

 

[cannongeorge]

AKAMAC/PJ: I had a problem parallelling two standby Detroit Diesel gensets, the new ones (MTUs) 2,000 kW ea, sub-transient reactance issues and a very touchy electronic govenor, (only ours and one other in the entire US) plus we were driving big VFDs with nasty harmonics out to the 64th octave..... One of our electrical engineers came up with a "beer" analogy that seemed to explain some things to us non-imaginary-number-complex-math types. --- and we fixed the issues. (Those imaginary numbers can really "bite!")



It sounds like you guys are running Natural Gas Waukesheshas... I've had a lot of (unwanted) experience lately regarding catalysts and emissions compliance... Are you using DSL or Johnson-Matthey? I think Livermore is in the BAQMD? as in non-methane (like ethane) pollutant level restrictions? Good Luck!



I am out of my office (offshore oilrig) for God knows how long but when I return I will look for the beer analogy and send it to you.



Ropinfool, I know a lead designer and Chief electrical engineer that both live in or near Temecula. Probably would like to chat with you-

 

[Peter Campbell]

Heres one we use for our operators- In an isloated buss operation, increasing speed setting increases frequency. When on the system the increased speed setting increases load. In an isolated buss increasing voltage regulator increases voltage, on the system increasing voltage increases lagging vars. The vars that your plant uses are fixed by the equipment operating. How is the synchroscope and the voltage metering laid out? are they usefull? It looks like the relaying is set up to prevent you from exporting power( reverse power). This is a function also of network protectors. At our plant we provide vars to the utility as well as power Normally 1,000 MWE, and vars between - 40 MVARS to 560 MVars. This takes a lot of exitation to do this. Exitation goes from a low 0f 3600 DC amps at 260 volts ( under 1 MW ) to 6000 DC amps at 480 Volts - just short of 3 MW exitation. The concerns are in the lead the generator can heat the stator core, in the lag the current is too high on the field for the cooling gas flow. If anyone out there can explain in human terms negative sequence i would like to know also!